The present invention concerns a process for refining a metal bath by oxygen blowing, particularly a molten-metal liquid bath containing a relatively high percentage of cold solid substances, notably of scrap.
The processes for refining of the melt by oxygen blowing permit, as is known, the incorporation of a greater or smaller amount of scrap or possibly of ore. The importance of this addition of cooled substances is dependent on the essential production of a quantity of thermal energy available in order to assure their melting.
In the processes for refining by means of oxygen blowing the thermal energy evolved derives in part from the exothermic reactions resulting from the oxidation of oxidizable elements contained in the melt, so that the incorporated amount of solid substances is a function of the content of C, Si, P, Mn charged in the melt.
Moreover, the release, in the course of the decarbonization of the melt, of CO which can occur according to the conditions developed in the converter, more or less favors a combustion. This after-combustion exothermic reaction constitutes a supplemental source of energy which one can seek to utilize to increase the rate of consumption of the scrap incorporated in the load.
The efforts with an eye to better exploitation of the energy sources present in the charged load, rather than to have recourse to outside energy, the costly contribution of which reduces the savings realizable through the augmentation of added scrap, have given birth to variants in the technology of oxygen blowing.
Thus it is, for example, known to augment the rate of combustion of CO above the molten bath in the course of the oxygen blowing process by increasing the quantity of oxygen available in the immediate proximity of the surface of the bath and outside the central blowing zone to a high level. One can obtain this increase thanks to supplemental oxygen blowing, subdivided in a plurality of jets covering a zone appreciably annular, which permanently cover the largest possible part of the surface of the bath. For the execution of this technique it is necessary to dispose special nozzles outside the primary nozzles and occasionally several secondary nozzles are present auxiliary at specific angles of inclination, adapted to the dimensions and shape of the converter.
Notwithstanding the use of special costly lances to increase the rate of after-combustion of CO near the surface of the bath, all imaginable efforts to increase the temperature near the surface of the bath for the purpose of melting an excess of scrap, are opposed by the presence at the surface of the bath of a layer of thick and foaming slag which forms on top of the bath in the course of refining by oxygen blowing and which acts like a thermal insulator thanks to its foaming consistency.
The purpose of this invention therefore is to propose a refining procedure permitting an increase in the traditional time for adding solid scraps while wholly avoiding the described disadvantages.